Seasonal Adaptations to Day Length in Ecotypes ofDiorhabdaspp. (Coleoptera: Chrysomelidae) Inform Selection of Agents Against Saltcedars (Tamarixspp.)

Abstract

Seasonal adaptations to daylength often limit the effective range of insects used in biological control of weeds. The leaf beetle Diorhabda carinulata (Desbrochers) was introduced into North America from Fukang, China (latitude 44° N) to control saltcedars (Tamarix spp.), but failed to establish south of 38° N latitude because of a mismatched critical daylength response for diapause induction. The daylength response caused beetles to enter diapause too early in the season to survive the duration of winter at southern latitudes. Using climate chambers, we characterized the critical daylength response for diapause induction (CDL) in three ecotypes of Diorhabda beetles originating from 36, 38, and 43° N latitudes in Eurasia. In a field experiment, the timing of reproductive diapause and voltinism were compared among ecotypes by rearing the insects on plants in the field. CDL declined with latitude of origin among Diorhabda ecotypes. Moreover, CDL in southern (<39° N latitude) ecotypes was shortened by more than an hour when the insects were reared under a fluctuating 35-15°C thermoperiod than at a constant 25°C. In the northern (>42° N latitude) ecotypes, however, CDL was relatively insensitive to temperature. The southern ecotypes produced up to four generations when reared on plants in the field at sites south of 38° N, whereas northern ecotypes produced only one or two generations. The study reveals latitudinal variation in how Diorhabda ecotypes respond to daylength for diapause induction and how these responses affect insect voltinism across the introduced range.

Population dependent effects of photoperiod on diapause related physiological traits in an invasive beetle (Leptinotarsa decemlineata)

“…This adaptation has been rapid as estimates of divergence in the critical photoperiod among populations were high and the species has expanded its range from sub-tropical to almost sub-arctic latitudes in a time span which in ecological and certainly in evolutionary terms could be called short. Thus my results lend support to the hypothesis that photoperiodic synchronization is a major eco-evolutionary factor in determining range expansion success (Bradshaw & Holzapfel 2007, Saikkonen et al 2012, see other invasive species in: Dalin et al 2010, Sadakiyo & Ishihara 2012, Urbanski et al 2012. My results furthermore support conclusions made previously that the L. decemlineata adult in diapause seems to be the ecophysiological stage facing the hardest selection at high latitude (Valosaari et al 2008).…”

“…While there are some examples of rapid photoperiodic adaptation (e.g. , Gomi 2007, Dalin et al 2010, Urbanski et al 2012, the actual molecular and physiological mechanisms of photoperiodic adaptation are still largely unclear (Bradshaw & Holzapfel 2007, Kostal 2011). There is a demand for more research in this area since it is becoming increasingly clear that photoperiodic adaptation is an important driver during range expansion since it allows species to re-synchronize lifehistory and stress tolerance related traits with novel phenology (Tauber et al 1986, Nelson et al 2010.…”

Molecular Genetic and Hybridization Studies ofDiorhabdaspp. Released for Biological Control ofTamarix

“…The revision of the Diorhabda species complex based on morphological (Tracy and Robbins 2009) and now molecular traits has helped provide a biological basis for host specificity (Dalin et al 2009;Herr et al 2009) and other developmental and physiological differences among Diorhabda species used in the tamarisk biological control program (Dalin et al 2010). Molecular methods will now be essential to track hybridization and introgression in the field.…”

“…In addition to safety testing, the new ecotypes were screened for traits that might make them more effective in areas where the original releases had been ineffective. New ecotypes were found to be better adapted to southern Tamarix phenology, as well as to photoperiod regimes found in the southernmost ranges of Tamarix in North America (Dalin et al 2010;Dudley et al 2006;Milbrath et al 2007). The ecotype collected from Crete, Greece, was shown to establish on T. parviflora whereas the Fukang, China, ecotype had failed (Carruthers et al 2008;Thomas et al 2009).…”

Mating Status Influences Cold Tolerance and Subsequent Reproduction in the Invasive Ladybird Harmonia axyridis

“…The ability to pass through cold conditions may be instrumental for the establishment of species introduced into a temperate or polar region (Dalin et al, 2010). Indeed, the more individuals able to overwinter, the more quickly a population can build-up the following spring.…”